1. Field of the Invention
The present invention relates to an absorbent article having a layer of continuous filaments disposed on a liquid receiving side to achieve good fitting feeling, and a manufacturing process thereof.
2. Description of the Related Art
Absorbent articles, such as sanitary napkin, disposable diaper or the like are typically of construction in which an absorbent layer is laid over a liquid impermeable backing sheet, and a liquid permeable surface material is laid over the liquid receiving side of the absorbent layer.
Conventionally, as the surface material of the absorbent article, use has been made of a non-woven fabric, such as a thermal bonded non-woven fabric in which thermoplastic synthetic fibers are bonded by hot embossing or by applying hot air, or a spun laced non-woven fabric in which fibers are entangled (interlaced) by applying water flow. With the fibers being bonded or entangled, these non-woven fabrics have a predetermined surface strength, while maintaining a sufficient bulkiness and permeability to liquid.
Moreover, as the surface material, it is also known in the art to use a synthetic film or non-woven fabric formed with a large number of through holes.
The surface material of the absorbent article is required to be excellent in liquid permeability to the absorbent layer, to have low possibility of causing so-called re-wetting back (the phenomenon in which the liquid once absorbed in the absorbent layer leaks back through the surface material to the surface of the absorbent article), and to be less irritative to the wearer""s skin contacting with the surface material.
Irritation on the skin is affected by following ability of the material located on the surface of the surface material to motion of the skin. For example, the surface of the surface material formed of the porous film (i.e., the film formed with through holes) has low following ability to motion of the skin to possibly cause irritative feeling to the skin of a wearer.
On the other hand, the non-woven fabric provides relatively less irritation to the skin, because its fibers contacting with the wearer""s skin may slightly move to follow the motion of the skin. In the nonwoven fabric formed with the through holes, too, since the fibers around the through holes may slightly move to follow the motion of the wearer""s skin, it provides relatively less irritation to the skin. However, the absorbent article employing the surface material formed of a non-woven fabric is less effective in view point of re-wetting back prevention performance in comparison with the porous film.
As set forth above, neither the non-woven fabric nor the porous film could satisfy all the functions required for the surface material of the absorbent article. Therefore, it has been difficult to provide a surface material satisfying all the required functions.
The present invention has been worked out in view of the shortcoming in the prior art set forth above. Therefore, it is an object of the present invention is to provide an absorbent article which has a surface layer of a structure less irritative to the skin of a wearer and achieving high performance in restricting re-wetting back, and a manufacturing process therefor.
According to a first aspect of the invention, there is provided an absorbent article comprising: a liquid permeable surface layer; a backing sheet; and an absorbent layer interposed between the surface layer and the backing sheet, the surface layer including a liquid permeable base and a layer of continuous filaments extending substantially in one direction and disposed on the surface of the base, the continuous filament layer being fixed to the base at a plurality of fixing portions which are spaced apart in the filament extending direction by a given pitch, to thereby form loop portions of the continuous filaments between adjacent fixing portions, the loop portions being raised toward the surface side.
Preferably, the fixing portions are arranged in a pattern of rows each extending in the filament extending direction, wherein in any two rows adjacent in a direction perpendicular to the fiber extending direction, fixing portions in one row are not continuous to but are offset from fixing portions in the other row, so that peaks of loop portions in one row are offset from peaks of loop portions in the other row for permitting each individual loop portion to behave independently of others.
It is possible that pitches of the fixing portions are differentiated at different positions of the article, and heights of the loop portions are varied depending upon the pitches of the fixing portions. In this case, loop portions having a greater height may be arranged at a center portion in a liquid absorbing region of the absorbent article, and loop portions having a smaller height may be arranged at front and rear sides of the center portion and/or at left and right sides of the center portion.
It is also possible that loop portions having a greater height and loop portions having a smaller height are alternated in the filament extending direction.
It is further possible that each fixing portion is formed as a bent or curved fixing line, and a distance between two fixing lines adjacent in the filament extending direction varies depending upon a shape of the fixing lines, so that each loop portion per se varies in height at different positions thereof.
It is still further possible that the continuous filament layer is consisted of a plurality of rows of continuous filaments, each row extends in straight to have a predetermined width, and the rows are spaced apart in a direction perpendicular to the filament extending direction. In this case, the base is preferably a porous sheet.
Preferably, a height of the loop portion from the surface of the base is greater than a pitch between adjacent fixing portions defining the loop portion. Also preferably, between adjacent fixing portions, a total length of continuous filaments appearing on the outer surface of the loop portion is 1.1 to 4 times of the pitch of the fixing portions.
For example, the base is contracted in the filament extending direction after formation of the fixing portions, so that an initial pitch between adjacent fixing portions is shortened by contraction of the base into the given pitch for raising the loop portions.
For contraction of the base, the base may be formed of a stretchable material or a heat shrinkable material. Alternatively, the absorbent article may further comprise an elastic member fitted on the base for causing contraction.
According to a second aspect of the invention, there is provided a manufacturing process of an absorbent article having a surface layer, a backing sheet, and an absorbent layer interposed between the surface layer and the backing sheet, comprising the steps of:
(a) fitting a longitudinally stretched elastic member over one surface of a liquid permeable base;
(b) simultaneously with the step (a) or before or after the step (a), stacking a layer of continuous filaments extending substantially in one direction on the other surface of the base and fixing the continuous filament layer to the base at a plurality of fixing portions which are spaced apart in the filament extending direction by a given initial pitch;
(c) causing contraction of the base in the filament extending direction to shorten the given initial pitch into a given contracted pitch by releasing stretching force on the elastic member for raising the continuous filaments in each region between adjacent fixing portions from the surface of the base to form loop portions, and whereby forming the surface layer; and
(d) laminating the surface layer, the backing sheet on opposite surfaces of the absorbent layer for forming the absorbent article.
According to a third aspect of the invention, there is provided a manufacturing process of an absorbent article having a surface layer, a backing sheet, and an absorbent layer interposed between the surface layer and the backing sheet, comprising the steps of:
(a) longitudinally stretching a liquid permeable, stretchable base;
(b) simultaneously with the step (a) or after the step (a), stacking a layer of continuous filaments extending substantially in one direction on the base and fixing the continuous filament layer to the base at a plurality of fixing portions which are spaced apart in the filament extending direction by a given initial pitch;
(c) causing contraction of the base in the filament extending direction to shorten the given initial pitch into a given contracted pitch by releasing stretching force on the base for raising the continuous filaments in each region between adjacent fixing portions from the surface of the base to form loop portions, and whereby forming the surface layer; and
(d) laminating the surface layer, the backing sheet on opposite surfaces of the absorbent layer for forming the absorbent article.
According to a fourth aspect of the invention, there is provided a manufacturing process of an absorbent article having a surface layer, a backing sheet, and an absorbent layer interposed between the surface layer and the backing sheet, comprising the steps of:
(a) supplying a heat shrinkable base;
(b) stacking a layer of continuous filaments extending substantially in one direction on the base and fixing the continuous filament layer to the base at a plurality of fixing portions which are spaced apart in the filament extending direction by a given initial pitch;
(c) causing heat shrinkage of the base in the filament extending direction to shorten the given initial pitch into a given contracted pitch by applying a heat on the base for raising the continuous filaments in each region between adjacent fixing portions from the surface of the base to form loop portions, and whereby forming the surface layer; and
(d) laminating the surface layer, the backing sheet on opposite surfaces of the absorbent layer for forming the absorbent article.
The manufacturing processes as set forth above may further comprise a step of opening a tow which is a bundle of crimped continuous filaments for forming the continuous filament layer. In addition, the manufacturing processes may further comprise a step of spreading the continuous filament layer in its width direction to have a uniform bulk, after the step of opening.